1. Field of the Invention
This present invention relates to filtering devices and clamps. More particularly, the invention relates to centrifuges which utilize a screen to separate a solid from a liquid and for clamps to secure the centrifuges.
2. Description of the Related Art
A conventional sugar refining process employs a centrifuge to separate sugar crystals out of raw molasses. The centrifuge includes a spinning drum having a truncated conical basket, which tapers towards its bottom. The walls of the truncated conical basket are lined with a screen material. In a typical sugar refining process, a raw molasses product containing sugar crystals is poured into the center of a centrifuge spinning at a very high ratexe2x80x94e.g. 1750 rpm. As the raw product containing sugar crystals is poured into the center of the centrifuge, inertia pushes the raw molasses through the screen material, through the basket, and out of the centrifuge. However, the sugar crystals are too big to pass through the screen and are left behind. As the raw molasses pass through the screen, the spinning of the centrifuge forces the sugar crystals up the walls of the centrifuge. The sugar crystals work their way up the screen, eventually passing up and over the perimeter of the screen. In this way, sugar crystals are filtered out of liquid raw molasses product and are collected as they pass over the lip of the spinning screen.
To separate sugar crystals from raw product, the screen employed must be very fine. That is, the openings in the screen must be very small to prevent the sugar crystals from passing through the screen along with the liquid, raw molasses. Conventional sugar processing screens have been formed by xe2x80x9cetchingxe2x80x9d a very thin metal plate. A metal plate may be etched with openings sized small enough to separate sugar crystals from liquid molasses. For example, a metal plate may be etched with a laser to form very small slits in the plate. The plate is then formed into a conical shape which fits within the walls of a centrifuge basket.
The greater the number of slits cut into a conventional sugar processing screen, the greater the xe2x80x9copen areaxe2x80x9d of the screen. A large number of slits, spaced closely together, produces a relatively large xe2x80x9copen areaxe2x80x9d in the screen, which increases the screen""s production. However, the slits in a typical sugar processing screen weaken the overall screen and subject it to fatigue. Additionally, sugar crystals may lodge in the slits of a conventional sugar processing screen, thereby reducing its performance. A sugar processing device having a screen which is durable and has a fine opening, high open area would be welcomed by those in the sugar processing industry. Additionally, other industries that utilize such processes as coal dewatering and driller mud dewatering, etc. would welcome a fine opening, high open area centrifuge screen.
Typically, the conventional sugar processing screen is secured in the truncated conical basket by a clamping ring. A conventional centrifuge 200 is shown in FIG. 12. In particular, FIG. 12 shows a partial cross sectional perspective view of a sugar processing screen 202, a conical basket 204 and a clamping ring 206. The clamping ring 206 is constructed to clamp a lower portion 208 of the conventional sugar processing screen 202 to the truncated conical basket 200 while an upper portion 210 of the conventional sugar processing screen may move freely. In this arrangement, the frictional force created by the clamping ring holds the conventional sugar processing screen in place in the centrifuge. However, a problem associated with the sugar refining process occurs while the centrifuge is spinning at a very high rate of speed. Specifically, the forces created by the centrifuge overcome the clamping force of the clamping ring. At this point, the conventional sugar processing screen begins to slide out of the clamping ring and subsequently flings out of the truncated conical basket, which may cause damage to the equipment or injury to nearby personnel.
There is a need, therefore, for an improved clamping ring arrangement that will secure a screen in conical basket. There is a further need for a clamping ring arrangement that will prevent the screen from falling out while the centrifuge is spinning at a very high rate of speed. There is yet a further need for a more reliable centrifuge screen.
According to the present invention, a centrifuge screen clamp is provided.
One embodiment provides a centrifuge screen clamp. The clamp comprises a body adapted to be secured to a centrifuge and a screen retaining portion connected to the body. The screen retaining portion comprises a pressure-generating-centrifuge-screen engaging surface adapted to engage a centrifuge screen and apply a force thereto to create a pressure fit; and an interface member engaging surface adapted to engage a corresponding interface portion disposed on the centrifuge screen and create an interference fit therewith, whereby the clamp interface member engaging surface and the clamp engaging surface create equal and opposite forces coplanar with a sliding tendency direction of the screen during rotation.
Another embodiment provides a centrifugal refining device. The centrifugal refining device comprises a rotatable support basket, a screen disposed in the basket for filtering a liquid during rotation of the drum, a clamp interface member rigidly disposed on the screen and defining a clamp engaging surface, and a clamp to secure the screen with respect to the rotatable support basket. The clamp comprises a body and a screen retaining portion connected to the body. The screen retaining portion comprises a pressure-generating-centrifuge-screen engaging surface disposed against the screen and applying a force thereto to create a pressure fit; and a clamp interface member engaging surface disposed against the clamp engaging surface to create an interference fit therewith, whereby the clamp interface member engaging surface and the clamp engaging surface create equal and opposite forces coplanar with a sliding tendency direction of the screen during rotation.
Yet another embodiment provides a centrifugal sugar refining device. The centrifugal sugar refining device comprises a rotatable drum defining an interior space, a rotatable support basket disposed at least partially in the interior space, a screen disposed in the basket for filtering sugar crystals from molasses during rotation of the drum, a clamp interface member rigidly disposed on the screen and defining a clamp engaging surface and a clamp to secure the screen with respect to the rotatable support basket. The clamp comprises a body and a screen retaining portion connected to the body. The screen retaining portion comprises a pressure-generating-centrifuge-screen engaging surface disposed against the screen and applying a force thereto to create a pressure fit; and a clamp interface member engaging surface disposed against the clamp engaging surface to create an interference fit therewith, whereby the clamp interface member engaging surface and the clamp engaging surface create equal and opposite forces coplanar with a sliding tendency direction of the screen during rotation.
In one embodiment, a clamp of the present invention secures a screen comprising a series of fine filter wires spaced closely together and mounted generally perpendicularly to a series of underlying support rods. In particular embodiments, the filter wires have a V-shaped profile with a width of approximately 0.020 inches. The mating points of the support rods also have a V-shaped profile with a width of approximately 0.060 inches. The filter wires are spaced approximately 0.0035 inches apart and the support rods are spaced approximately 0.38 inches apart. However, it will be understood by one of ordinary skill in the art that different dimensions may be used to create a fine opening, high open area centrifuge screen used, for example, to separate crystalline sugar from liquid raw molasses.